8 parts per million is likely to represent the correct reading for the region. Hence the correct option is a.
Measuring carbon monoxide in parts per million (ppm) is a standard practice in environmental monitoring and air quality assessment. This unit expresses the ratio of carbon monoxide molecules to one million molecules of air, providing a comprehensive and standardized measure for the concentration of this harmful gas. It allows researchers and policymakers to evaluate and compare pollution levels across various regions and over different time frames.
Using units like liters, meters per second, or milliseconds would be inappropriate for expressing the concentration of a gas in the atmosphere, as these units pertain to volume, speed, and time, respectively, and do not convey the proportional relationship needed for assessing air quality. Therefore, when examining the distribution of carbon monoxide, a reading of 8 parts per million is a meaningful and relevant representation of the gas concentration in the specified region. Hence the correct option is a.